The fan is a kind of machinery that relies on input to increase the pressure of gases and to discharge them .It is widely used in ventilation, dust removal and cooling of building, mines, tunnels, cooling towers, vehicles, ships and buildings Ventilation and draught of boilers and industrial furnaces;Cooling and ventilation in air conditioning equipment and household electrical equipment;Drying and selecting of grain;Inflation and propulsion of Wind tunnel air source and hovercraft According to the direction of gas flow, fans can be divided into centrifugal, axial, oblique flow (mixed flow) and cross-flow.